1. Field of the Invention
The present invention relates generally to a process of continuous casting of a molten metal. More specifically, the invention relates to a technique for detecting of possible break out of cast metal in continuous casting and prevention thereof. The invention also relates to a device for precisely measuring temperature of the casting mold, which is applicable for detection of possible break out of the cast metal.
2. Description of the Background Art
Conventionally, various approaches have been taken for detecting possibility of break out of cast metal in a continuous casting process. In general, the conventionally proposed method of detection of break out of the cast metal takes the temperature variation of the casting mold as a parameter for detection of break out. For example, Japanese Patent First (unexamined) Publication (Tokkai) Showa No. 57-115961 discloses a method, in which temperature of a continuous casting mold is measured at temperature measuring points which are mutually different from each other in the drawing direction. The measured temperatures are compared to each other for detecting temperature variation and thereby detect possibility of break out in a cast metal. On the other hand, Japanese Patent second (examined) Publication (Tokko) Showa No. 56-7783 discloses a method of detection of possible break out by detecting temperature difference in copper walls of a casting mold. Furthermore, Japanese Patent First Publication (Tokkai) Showa No. 57-152356 discloses employment of a thermometric couple disposed in the wall of the casting mold. In the method of Tokkai Showa No. 57-152356, possible break out is detected when the measured temperature once rises above an average temperature and subsequently drops below the average temperature.
Such conventional methods of detection of break out were not complete and not satisfactory due to the following defects. Namely, the temperature of the casting mold is variable depending upon the casting speed to rise according to increasing casting speed and to lower according to decreasing casting speed. Therefore, there is a possibility of mis-detection of the break out of the cast metal when the casting speed fluctuates.
In addition, the detection of break out of the cast metal can be inaccurate when uneveness of powder to be introduced between the casting mold wall and the cast metal exists, or when formation of an air gap occurs.
In order to avoid the defects in the aforementioned prior art, there are some proposals for improvement in detection of the possible break out of the cast metal. For example, Japanese Patent First Publication (Tokkai) Showa No. 60-44163 discloses a method of detection of the break out, in which casting mold wall temperatures are measured at least at two measuring points. Judgement of possibility of break out is made when the measured temperatures at two measuring points are inclined to the higher temperature side in relation to a normal temperature level for a given period of time. On the other hand, Japanese Patent First Publication (Tokkai) Showa No. 61-289954 utilizes a plurality of set reference temperatures to be compared with the measured temperature data for detecting the break out. Japanese Patent First Publication (Tokkai) Showa No. 61-226154 utilizes preset data comparing the wall temperature of the casting mold versus casting speed. Utilizing the preset data, a data component in the temperature data influenced by variation of the casting speed can be successfully avoided. Then, the temperature data at one selected measuring point is compared with that obtained from remaining measuring points. In this Tokkai Showa No. 61-226154, judgement of possible break down is made when the relative temperature between the selected measuring point and the remainder bocomes greater than an upper limit or smaller than a lower limit.
In case of the technique shown in Tokkai Showa No. 60-44163, break out cannot be detected when casting speed is continuously varying or meniscus fluctuating. On the other hand, the method of Tokkai Showa No. 61-289954, increases possibility of mis-detection unless the set reference temperatures are adapted to the casting conditions. Therefore, in such case, set reference temperatures have to be differentiated depending upon the casting conditions. In case of Tokkai Showa No. 61-226154, since it requires precise measurement of parameters adapted to positions of the temperature measurement and casting condition, setting has to be adjusted every time the temperature measuring points are differentiated or the casting condition is changed.